9Brassil J, Low S, Maxemchuk N F, et al. Electronic marking and identification techniques to discourage document copying[ J]. IEEE Journal on Selected Areasin Communications, 1995,13 (8) : 1495 - 1504.
10B rassil J, Low S, M axem chuk N F. Copy right protection for the electronic distribution of text documents [ J ]. Proceedings of the IEEE, 1999,87(7) :1181 -1196.